Between 1981 and 1990, the American Red Cross Rare Donor Registry supplied 9,872 units of red cell components with rare phenotypes to blood centers in the United States and abroad. Approximately 51% were from donors with high-frequency antigen-negative phenotypes and 49% were from donors with multiple antigen-negative phenotypes. Since 1989, the disease category requiring the largest number of units has been sickle cell disease. Strategies to ensure that the Registry will have adequate resources to meet future requirements include testing selected donors for rare phenotypes and blood conservation programs, such as intraoperative salvage and the treatment of anemia of chronic renal failure with recombinant erythropoietin.